Custom HTML templates

[tylerjpeterson]

Resolves #33 by allowing users to provide a path to a custom markup template when rendering output as html. More specifically:

• updated README.md with a list of variables that can be used within a custom template
• updated main.js with the -t, --template option to use a custom html
• updated cli.js to use template set in user config, otherwise defaults to existing template
• imported fs from cli.js to confirm existence of custom template, otherwise throws an error
• tests are passing

I realize this means your authorship may no longer appear in the generated output, so I fully understand if you're not comfortable accepting this PR.
Thanks!

[rtfpessoa]

@tylerjpeterson thanks for your contribution.

The only thing I am worried is the flag name since the diff2html library already has a template parameter that represents the actual templates of the diff and I think this would be confusing.

This template is a different thing that I never migrated to hogan.js and is still using a hardcoded replaces. What do you think of changing the name to html-wrapper-template, or wrapper-template?

[tylerjpeterson]

@rtfpessoa - makes sense to me - I'm happy to update the flag. I'll try to get to it sometime this evening. Thanks!

[tylerjpeterson]

@rtfpessoa - had a chance to update it now. Sorry for the sloppy commits, I didn't realize there was support for multi-character flags (which further reduces chance of confusion / collision with other dependencies). Let me know if this requires further updates.

[rtfpessoa]

Released as https://github.com/rtfpessoa/diff2html-cli/releases/tag/v2.6.0

[dpetrov]

Thanks @rtfpessoa, release looks good and thanks for the help.